The present invention relates to a method of and an apparatus for laminating and pressing a plurality of thermoplastic sheets such as SMC sheets or the like which will be rendered adhesive when heated.
Recently, automobiles are composed of many parts which are made up of laminated and pressed thermoplastic sheets such as SMC sheets, stampable sheets, or the like that comprise glass fibers, carbon fibers, etc., impregnated with thermoplastic resin. These parts of laminated thermoplastic sheets are used in place of metallic parts for their smaller weight and easy assembling capability. If an automobile component requiring a high mechanical strength such as a bumper beam, for example, is to be fabricated of such sheets, a plurality of thermoplastic sheets are heated until they are sufficiently softened, and then put together into a laminated assembly which is thereafter pressed to shape by a shaping die assembly of a shaping device.
The sheets are made adhesive or sticky when they are softened with heat. Therefore, when these sheets are to be stacked into a laminated assembly or the laminated assembly is to be brought between the shaping dies, the sheets cannot be held by a vacuum attracting device which is usually employed to handle steel sheets.
One known holder device for holding such thermoplastic sheets has needles for penetrating the sheets as disclosed in Japanese Laid-Open Utility Model Publication No. 58-194009 and Japanese Utility Model Publication No. 58-50987. Thermoplastic sheets, which have been heated individually, are successively penetrated by the needles so that the sheets are put together as a laminated assembly, and the laminated assembly is held by the needles. Then, the holder device is moved into a position between the shaping dies, and then the needles are removed from the sheets to leave them in the shaping device.
The disclosed holder device is however disadvantageous for various reasons. Since the sheets are successively held one by one, the efficiency is low. The needles have to be large in diameter for required mechanical strength because the laminated assembly is supported by the needles. If the needles are of a larger diameter, however, large holes are formed in the sheets, thus damaging some fibers of the sheets and lowering the mechanical strength of the final product. Inasmuch as the sheets that are held by the needles are flexed by gravity because they are softened, the holes formed by the needles are enlarged, further impairing the mechanical strength of the shaped product. When the laminated assembly is placed in the shaping die assembly, air may be trapped between the sheets, and any such trapped air will make the shaped product less strong.